Cryptographic Security Characteristics of 802.11 Wireless LAN Access Systems
draft-orr-wlan-security-architectures-00
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Stephen Orr
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Anthony Grieco
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Dan Harkins
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Network Working Group S. Orr
Internet-Draft A. Grieco
Intended status: Informational Cisco Systems, Inc.
Expires: April 18, 2013 D. Harkins
Aruba Networks
October 15, 2012
Cryptographic Security Characteristics of 802.11 Wireless LAN Access
Systems
draft-orr-wlan-security-architectures-00
Abstract
This note identifies all of the places that cryptography is used in
Wireless Local Area Network (WLAN) architectures, to simplify the
task of selecting the protocols, algorithms, and key sizes needed to
achieve a consistent security level across the entire architecture.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 18, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used In This Document . . . . . . . . . . . . . . 4
3. Architectures . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Standalone WLAS . . . . . . . . . . . . . . . . . . . . . 5
3.3. Centralized WLAS . . . . . . . . . . . . . . . . . . . . . 5
3.4. Architectural Commonality . . . . . . . . . . . . . . . . 6
4. WTP to Access Controller Service Cryptographic Security . . . 7
5. Client to AAA Service Cryptographic Security . . . . . . . . . 8
5.1. EAP Method . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Pre Shared Key, or Password, Method . . . . . . . . . . . 8
6. Authenticator to AAA Service Cryptographic Security . . . . . 9
7. Wireless Link Layer Cryptographic Security . . . . . . . . . . 10
8. Cryptographic profiles . . . . . . . . . . . . . . . . . . . . 11
8.1. DTLS and TLS . . . . . . . . . . . . . . . . . . . . . . . 11
8.2. X.509 Certificates . . . . . . . . . . . . . . . . . . . . 13
8.3. Link Layer Encryption . . . . . . . . . . . . . . . . . . 14
8.4. AAA . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.5. IPSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9.1. Algorithm Choices . . . . . . . . . . . . . . . . . . . . 19
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
12.1. Normative References . . . . . . . . . . . . . . . . . . . 22
12.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
Wireless LAN Access Systems (WLAS) are complex systems that involve
interworking many technology components defined by various standards
bodies. To ensure that the entire system is secure against
sophisticated, persistent, and well-funded adversaries, each
component MUST use strong cryptography. However, the architectural-
level cryptographic capabilities and relationships between the
various protocols and security mechanisms provide by each of the WLAS
architecture components have not been documented.
In this note, we define a series of architectures based on common
wireless LAN standards; IEEE 802.11 [IEEE.802-11.2012], Control and
Provisioning of Wireless Access Points [RFC5415], RADIUS [RFC2865],
IEEE 802.1x [IEEE.802-1X.2010], and the Extensible Authentication
Protocol [RFC5247]. Within each of these architectures, we describe
the uses of cryptography and in doing so, we capture an overall
understanding of the cryptographic security of the Wireless LAN
Access Systems. This document can also serve as a framework for
future specifications to define profiles that specify particular
cryptographic algorithms at each area of the architecture creating
detailed specifications for interoperability with well understood
cryptographic security properties.
This document does not define new protocols, nor cryptographic
algorithms.
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2. Conventions Used In This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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3. Architectures
3.1. Overview
The Wireless LAN Access System (WLAS) architectures discussed in this
document describe host/user and network authentication, over the air
security, as well as various methods for managing the backend
processes to support that wireless LAN access system. These backend
processes include both distributed as well as non-distributed
infrastructures for doing access control, authentication and Radio-
Frequency management.
3.2. Standalone WLAS
The Standalone WLAS consist of a Wireless Termination Point (WTP or
Access Point) and a client. The client contains an IEEE 802.1x
[IEEE.802-1X.2010] supplicant and the client side of an EAP method
[RFC3748]. The WTP contains an IEEE 802.1x [IEEE.802-1X.2010]
authenticator. An Authentication, Authorization and Accounting
Service (AAA), which incorporates the server side of at least one EAP
method [RFC3748], resides either on the WTP or as a stand-alone
server. This architecture is commonly deployed in small scale
environments such as consumer and commercial deployments, or in
places where backend resources are not available to provide a more
distributed architecture. If 802.1x authentication is not deployed
then 802.11 SAE authentication SHOULD be used for secure
authentication using a pre-shared key or password.
client(s) WTP AAA Service
|-------------(1)----------------|
|-------(2)-------|
|------(3)-----|
Figure 1: Standalone WLAS Architecture
Each of the lines in Figure 1 denotes communication that MUST be
secured. The numbers are defined in (Section 3.4). This notation is
used throughout this note.
3.3. Centralized WLAS
The Centralized WLAS is similar to the Standalone AP architecture
with the addition of an Access Controller (AC) to manage the
collection of WTP's. By moving the IEEE 802.1x [IEEE.802-1X.2010]
authenticator off the WTPs and centralizing it on the Access
Controller, this architecture allows for large scale deployments of
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secure wireless infrastructure. As with Section 3.2 the AAA service
can be incorporated on the AC or reside on a stand-alone server.
This architecture supports [RFC5415] for control and provisioning of
wireless access points (CAPWAP).
client(s) WTP Access Controller AAA Service
|-------(4)--------|
|------------------------(1)-------------------------|
|-------(2)---------|
|----(3a)------| or
|------------(3b)-----------------|
Figure 2: Centralized WLAS Architecture
3.4. Architectural Commonality
In each of the above architectures, there are necessary services that
we will describe in more details in the sections below. (1) describes
authentication and authorization communications that occurs between
the client and the AAA service in the form of an EAP method. (2)
describes additional communications that occurs in support of EAP, as
well as distribution of other keying material via the AAA service.
(3a) and (3b) describe the cryptographic security applied to
[IEEE.802-11.2012] frames. In (3a), the frames are terminated on the
WTP; in (3b) the frames are terminated on the AC. (4) Describes the
authentication and cryptography security between the WTP and the
access controller.
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4. WTP to Access Controller Service Cryptographic Security
Specific to the Centralized WLAS Architecture is the establishment of
a secure channel between the WTP and the AC. This command channel
MUST be secured to insure both confidentiality and integrity of the
communication between the AC and the WTP. The IETF has defined
CAPWAP [RFC5415] to communicate between the WTP and the AC but there
are other, proprietary, tunneling protocols to perform the same task.
However, standards based security protocols such as DTLS, TLS or
IPSEC MUST provide the authenticity and integrity assurance for
securing any tunneling or encapsulation mechanism.
There are two channels between the WTP and AC that need security--
the command and control channel; and, the data channel. Through the
command and control channel, the AC configures, queries and manages
the WTP, and the WTP reports status and airtime monitoring
information to the AC. Traffic sent between the client and the
network behind the AC goes through the data channel.
[RFC5415] defines using DTLS [RFC6347]to protect the control and data
channels. Other protocols such as IPSec [RFC4301] or TLS [RFC5246]
can also be implemented to secure the control traffic in addition to
the user data channel.
In order to establish secure connections between the WTP and AC
credentials MUST be deployed on each device. The most obvious choice
is an X.509 certificate which can be used to perform mutual
authentication with DTLS [RFC6347], IPsec [RFC4301] or TLS [RFC5246].
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5. Client to AAA Service Cryptographic Security
5.1. EAP Method
The [IEEE.802-11.2012]standard defines a Robust Security Network
(RSN). An RSN can utilizes IEEE 802.1x [IEEE.802-1X.2010] and the
Extensible Authentication Protocol [RFC3748], or it can use the SAE
protocol in [IEEE.802-11.2012] to provide authentication and key
management services between the client and WLAS. EAP Authentication
occurs between the client and the AAA service which may reside within
a component of the WLAS (WTP or AC) or as a standalone AAA Server.
It is not the intent of this document to specify the type of
transport for the authentication service (i.e RADIUS, Diameter
[RFC3588] etc) or the specific communication channel between the
Network Access Server (NAS) and the Authentication Service. Mutual-
Authentication is achieved through the establishment of a secure
channel for exchanging credentials between the client and the
Authentication Server utilizing an EAP method which satisfies the
requirements of [RFC4017]. The main output of the EAP process is the
generation of the Master Session Key (MSK) and Extended Master
Session Key (EMSK) known only to the Client (supplicant) and the AAA
server that will be used to generate the keying material for the
cipher suites. An in depth discussion on EAP Key management can be
found in EAP Key Management Framework document [RFC5247].
5.2. Pre Shared Key, or Password, Method
When 802.1X is not used, a pre-shared key or password/passphrase can
be used with the SAE protocol from [IEEE.802-11.2012] to perform the
mutual authentication and key management functions required by an
RSN. SAE employs a zero-knowledge proof protocol that allows the
client and WTC/AC to prove knowledge of a shared secret (PSK or
password or passphrase) without disclosing the secret. It is
resistant to off-line dictionary attack. The result of the SAE
protocol is a cryptographically strong PMK based on discrete
logarithm cryptography.
An alternative to SAE is the pre-shared KEY mode of
[IEEE.802-11.2012] referred to by the Wi-Fi Alliance as Wi-Fi
Protected Access Personal (WPA2-PSK). With WPA2-PSK, the pre-shared
key repeatedly hashed to directly generate a 256-bit PMK. This
technique should be avoided, though, as is susceptible to off-line
dictionary attack and numerous attack tools to subvert WPA2-PSK exist
on the Internet.
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6. Authenticator to AAA Service Cryptographic Security
As stated in the previous section, the byproduct of EAP
authentication is the generation of keying material to be used in the
cryptographic process between the client and the WTP to secure the
over the air communications. The AAA server generates the AAA key
which will be forwarded directly to the WTP in a Standalone WLAS, and
forwarded to the AC in a Centralized WLAS where they will generate
the Pairwise Master Key (PMK) (bits 0-255 of the AAA key). The
transmission of the AAA key needs to be protected between the AAA
server and the WTP or the AAA server and the AC depending on which
architecture is deployed. NIST has previously made recommendations
on securely encrypting plain text keying material for transport over
insecure media with AES Key Wrap [AES_Key_Wrap] as well as industry
with the Advanced Encryption Standard Key Wrap Algorithm [RFC3394].
In addition to the transport of the keying material it is suggested
that all AAA traffic between the Authenticator (WTP or AC) and the
Authentication Service (AAA) be secured by standards based methods
such as, but not limited to: IPSEC, TLS or DTLS.
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7. Wireless Link Layer Cryptographic Security
Upon completion of an authentication protocol, such as SAE or
[IEEE.802-1X.2010], the client and AC (or WTP) share a PMK. Since
the PMK may be been disclosed by an external AAA server to the AC (or
WTP) it is necessary to perform a key confirmation handshake.
[IEEE.802-11.2012] defines the 4-way Handshake to prove possession of
the PMK and to derive a transient session key, called the PTK, which
is used to secure the wireless link layer. During the 4-way
handshake, the WTP or AC also discloses a broadcast/multicast key,
called the GTK, to use for the wireless media.
Wireless link layer communication is protected through the Advanced
Encryption Standard Counter Mode with Cipher Block Chaining Message
Authentication Code Protocol (AES-CCMP). AES-CCMP is currently the
preferred cryptographic algorithm for both unicast and multicast/
broadcast traffic. The client is the source and sink of a secure bi-
directional data flow. The other end of that flow can be either the
WTP or the AC, depending on whether it is a standalone WLAS
(Section 3.2) or a centralized WLAS (Section 3.3), respectively.
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8. Cryptographic profiles
In each of the above architectural areas, there are a number of
different security protocols that serve various functions needed to
build secure wireless LAN architectures. Each protocol has important
choices to be made in context of this overall cryptographic security
within that protocol and subsequently has significant impacts to the
overall security parameters of the system. The security mechanisms
are summarized in Table 1.
+--------+------------+---------------+------------+----------------+
| | Client | WTP | AC | AAA |
+--------+------------+---------------+------------+----------------+
| Client | | 802.11 | 3rd Party; | EAP w/TLS |
| | | | 802.1x | |
| | | | Supplicant | |
+--------+------------+---------------+------------+----------------+
| WTP | 802.11 | | DTLS; | TLS, DTLS, |
| | | | IPSEC | IPSec, AES |
| | | | | KeyWrap |
| | | | | (Standalone |
| | | | | Architecture) |
+--------+------------+---------------+------------+----------------+
| AC | 3rd Party; | DTLS; IPSEC | | TLS, DTLS, |
| | 802.1x | | | IPSec, AES |
| | Supplicant | | | KeyWrap |
+--------+------------+---------------+------------+----------------+
| AAA | EAP w/TLS | TLS, DTLS, | TLS, DTLS, | |
| | | IPSec, AES | IPSec, AES | |
| | | KeyWrap | KeyWrap | |
| | | (Standalone | | |
| | | Architecture) | | |
+--------+------------+---------------+------------+----------------+
Table 1: Cryptographic Security Interactions
8.1. DTLS and TLS
TLS and DTLS are well studied and documented from a cryptographic
strength perspective and there are a number of works that create
profiles for TLS and DTLS and its use within systems of varying
security requirements. Table 2 provides an example of the
cryptographic functional requirements necessary to define a TLS
CipherSuite and associated security of each. When profiling against
this document, authors MUST define cryptographic algorithms for each
function in Table 2
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+-------------+----------+------------+---------------+-------------+
| Function | Example | Cryptograp | Algorithm | Cryptograph |
| | Algorith | h ic | Reference | i c Strengt |
| | m s | Strength | | h Reference |
+-------------+----------+------------+---------------+-------------+
| Authenticat | RSA 2048 | 112 | [RFC3447] | NIST SP |
| i on | | | | 800-57 |
| | | | | [NIST800-57 |
| | | | | ] |
+-------------+----------+------------+---------------+-------------+
| Key | ECC P256 | 128 | [RFC4492] | NIST SP |
| Exchange | | | | 800-57 |
| | | | | [NIST800-57 |
| | | | | ] |
+-------------+----------+------------+---------------+-------------+
| Payload | AES 128 | 128 | [FIPS.197.200 | NIST SP |
| Protection | CBC | | 1 ] | 800-57 |
| | | | | [NIST800-57 |
| | | | | ] |
+-------------+----------+------------+---------------+-------------+
| Message | HMAC-SHA | 128 | [NIST.PUB.198 | NIST SP |
| Auth | - 1 | | A ] | 800-57 |
| | | | | [NIST800-57 |
| | | | | ] |
+-------------+----------+------------+---------------+-------------+
Table 2: DTLS and TLS Cryptographic Security Algorithms
Throughout the Wireless LAN Access System, TLS and DTLS are used in a
number of different places. Someone profiling wireless architectures
might require alternative algorithm definitions for different uses of
TLS/DTLS in the architecture. One example might be a place that
describes using TLS or DTLS to protect the transport of an ephemeral
key vs its use to protect a long lived secret. In this case, a
profile might be willing to trade off less security of the
cryptographic algorithms for the ephemeral key.
Table 3 shows the places in the wireless architectures described in
Section 3 that TLS or DTLS can be used
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+---------------------+-----------+---------------------------------+
| Location in | Protocol | Used to Protect |
| Architecture | | |
+---------------------+-----------+---------------------------------+
| WTP To Access | CAPWAP | Management, session keys, user |
| Controller Service | using | traffic |
| (Section 4) | DTLS | |
+---------------------+-----------+---------------------------------+
| Client to AAA | EAP | session keys, authentication |
| Service (Section 5) | method | |
| | using TLS | |
+---------------------+-----------+---------------------------------+
| Authenticator to | DTLS/TLS, | Confidentiality and |
| AAA Service | IPSec | Authenticity of Radius traffic |
| (Section 6) | | (wrapped session keys) |
+---------------------+-----------+---------------------------------+
Table 3: DTLS and TLS Architectural Usage
8.2. X.509 Certificates
The security level provided by algorithm and key length choice for
X.509 Certificates is well studied solely in context of the
certificates itself. Table 4 lists the types of cryptographic
security functions used within X.509 Certificates and provides
examples for each. Any profile of Wireless LAN Architecture MUST
include definitions for each cryptographic security function used
within X.509 certificates.
+----------+-----------+--------------+-------------+---------------+
| Function | Example | Cryptographi | Algorithm | Cryptographic |
| | Algorithm | c Strength | Reference | Strength |
| | s | | | Reference |
+----------+-----------+--------------+-------------+---------------+
| Signatur | RSA with | 112 | [RFC3447] | NIST SP |
| e | 2048 bit | | | 800-57 |
| Algorit | public | | | [NIST800-57] |
| hm | keys | | | |
+----------+-----------+--------------+-------------+---------------+
| Public | RSA 2048 | 112 | [RFC3447] | NIST SP |
| Key | | | | 800-57 |
| Algorith | | | | [NIST800-57] |
| m | | | | |
+----------+-----------+--------------+-------------+---------------+
| Hash | SHA256 | 128 | [FIPS-180-3 | NIST SP |
| Function | | | ] | 800-57 |
| | | | | [NIST800-57] |
+----------+-----------+--------------+-------------+---------------+
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Table 4: X.509 Certificate Cryptographic Security Functions
Throughout the Wireless LAN Access System, X.509 certificates are
used in a number of different places. Table 5 shows the places in
the wireless architectures described in Section 3 that X.509
Certificates are potentially used
+----------------------+----------------+---------------------------+
| Location in | Protocol | Used to Protect |
| Architecture | | |
+----------------------+----------------+---------------------------+
| WTP To Access | DTLS used | Authenticity of |
| Controller Service | within CAPWAP; | Management, session keys, |
| (Section 4) | IPSec | user traffic |
+----------------------+----------------+---------------------------+
| Client to AAA | TLS (Example | Authenticity of session |
| Service (Section 5) | EAP Method) | keys, authentication |
+----------------------+----------------+---------------------------+
| Authenticator to AAA | DTLS, TLS or | Authenticity of AAA |
| Service (Section 6) | IPSec | traffic (wrapped session |
| | | keys) |
+----------------------+----------------+---------------------------+
Table 5: X.509 Architectural Usage
8.3. Link Layer Encryption
Link Layer encryption for Wireless LAN Access Systems is well defined
by the IEEE 802.11-2012 standard Future 802.11 standards need to
address link layer encryption as an integral part of the standard.
Current 802.11 standards require the implementation of 128 bit key
length.
+------------+-----------+------------+----------------+------------+
| Function | Example | Cryptograp | Algorithm | Cryptograp |
| | Algorithm | h ic | Reference | h ic |
| | s | Strength | | Strength |
| | | | | Referenc |
| | | | | e |
+------------+-----------+------------+----------------+------------+
| 802.1x 4 | AES Key | 128 | [IEEE.802-11.2 | NIST SP |
| Way | Wrap with | | 0 12] | 800-57 |
| Handshake | HMAC-SHA1 | | | [NIST800-5 |
| | - 128 | | | 7 ] |
+------------+-----------+------------+----------------+------------+
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+------------+-----------+------------+----------------+------------+
| Message | HMAC-SHA- | 128 | [NIST.PUB.198A | NIST SP |
| Authentica | 1 | | ] | 800-57 |
| t ion | | | | [NIST800-5 |
| | | | | 7 ] |
+------------+-----------+------------+----------------+------------+
| Pseudo-Ran | HMAC-SHA- | 128 | [NIST.PUB.198A | NIST SP |
| d om | 1 | | ] | 800-57 |
| Function | | | | [NIST800-5 |
| | | | | 7 ] |
+------------+-----------+------------+----------------+------------+
| 802.11 | AES-CCMP | 128 | [FIPS.197.2001 | NIST SP |
| Management | | | ] | 800-57 |
| Frame | | | | [NIST800-5 |
| Encryption | | | | 7 ] |
+------------+-----------+------------+----------------+------------+
| 802.11 | AES-CCMP | 128 | [FIPS.197.2001 | NIST SP |
| Payload | | | ] | 800-57 |
| Encryption | | | | [NIST800-5 |
| | | | | 7 ] |
+------------+-----------+------------+----------------+------------+
Table 6: Link Layer Security Algorithms
As a minimum, link layer encryption needs to be used in wireless
architectures as indicated in Table 7 to protect the data in transit.
When profiling against this document, authors MUST define
cryptographic algorithms for each function described in Table 7. In
addition to over the air link layer encryption, there are other
places where related, but different link layer encryption (i.e.
802.1ae) could be leveraged within the wireless architecture. Link
layer encryption in these alternative places MAY be profiled for use
in the overall cryptographic integrity of the system but are not
covered here.
+--------------+------------+---------------------------------------+
| Location in | Protocol | Used to Protect |
| Architecture | | |
+--------------+------------+---------------------------------------+
| Client to | AES-CCMP, | 802.1x 4-way handshake (stand alone |
| WTP | AES Key | configuration), 802.11 |
| (Section 7) | Wrap, | unicast/multicast data frames and |
| | HMAC-SHA-1 | Management Frame protection using the |
| | | Integrity Group Temporal Key (IGTK) |
+--------------+------------+---------------------------------------+
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+--------------+------------+---------------------------------------+
| Client to AC | AES-CCMP, | 802.1x 4-way handshake and optional |
| | AES Key | configuration where 802.11 |
| | Wrap, | unicast/multicast data frames and |
| | HMAC-SHA-1 | Management Frame protection using the |
| | | Integrity Group Temporal Key |
| | | (IGTK)encryption is performed on the |
| | | AC |
+--------------+------------+---------------------------------------+
Table 7: Link Layer Encryption Architectural Uses
8.4. AAA
It is strongly suggested that traffic between the WTP/AC and the AAA
service be secured to provide confidentiality and integrity of the
user/device being authenticated as well as the key data used for the
encryption process. The use of the well documented cryptographic
protocols IPSEC (Section 8.5), TLS or DTLS (Section 8.1) can be used
to protect traffic between the WTP/AC and the AAA service. When
profiling against this document, authors MUST define the
cryptographic algorithms for each function in listed in Table 8
+---------------+----------------+----------------------------------+
| Location in | Protocol | Used to Protect |
| Architecture | | |
+---------------+----------------+----------------------------------+
| Authenticator | TLS/DTLS or | Used to secure all |
| to AAA | IPSec | authentication traffic between |
| (Section 6) | | the Authenticator (WTP or AC) |
| | | and the AAA service |
+---------------+----------------+----------------------------------+
| Authenticator | AES Key Wrap | Used to encrypt only the key |
| to AAA | [AES_Key_Wrap] | data between the Authenticator |
| (Section 6) | | (WTP or AC) and the AAA services |
+---------------+----------------+----------------------------------+
| Client to AAA | EAP | Used to perform authentication |
| (Section 5) | | between Client and AAA server |
+---------------+----------------+----------------------------------+
Table 8: AAA Security Architectural Uses
8.5. IPSEC
IPSEC is well studied and documented from a cryptographic strength
perspective and there are a number of works that create profiles for
IPSEC and its use within systems of varying security requirements.
Table 9 provides an example of the cryptographic functional
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requirements necessary to define an IPSEC CipherSuite and associated
security of each. When profiling against this document, authors MUST
define cryptographic algorithms for each function in Table 9
+------------+-----------+------------+--------------+--------------+
| Function | Example | Cryptograp | Algorithm | Cryptographi |
| | Algorithm | h ic | Reference | c Strength |
| | s | Strength | | Reference |
+------------+-----------+------------+--------------+--------------+
| IKE | RSA 2048 | 112 | [RFC3447] | NIST SP |
| Authentica | | | | 800-57 |
| t ion | | | | [NIST800-57] |
+------------+-----------+------------+--------------+--------------+
| IKE | HMAC-SHA- | 256 | [RFC4868] | NIST SP |
| Pseudo-ran | 2 56 | | | 800-57 |
| d om | | | | [NIST800-57] |
| Function | | | | |
+------------+-----------+------------+--------------+--------------+
| IKE | Group 14 | 112 | [RFC3526] | NIST SP |
| Diffie-Hel | | | | 800-57 |
| l man grou | | | | [NIST800-57] |
| p | | | | |
+------------+-----------+------------+--------------+--------------+
| IKE Hash | SHA-256 | 128 | [FIPS-180-3] | NIST SP |
| | | | | 800-57 |
| | | | | [NIST800-57] |
+------------+-----------+------------+--------------+--------------+
| IKE | AES 128 | 128 | [FIPS.197.20 | NIST SP |
| Encryption | CBC | | 0 1] | 800-57 |
| | | | | [NIST800-57] |
+------------+-----------+------------+--------------+--------------+
| ESP | AES-CBC | 128 | [FIPS.197.20 | NIST SP |
| Encryption | | | 0 1] | 800-57 |
| | | | | [NIST800-57] |
+------------+-----------+------------+--------------+--------------+
| ESP | HMAC-SHA1 | 128 | [FIPS-180-3] | [NIST.PUB.19 |
| Integrity | | | | 8 A] |
+------------+-----------+------------+--------------+--------------+
Table 9: IPSEC Cryptographic Security Algorithms
IPSec in many cases has been superseded by other protocols for
security within the Wireless LAN Access System. However, IPSEC could
play a role and Table 10 describes places in the WLAN Access System
Architecture (Section 3) where it can be utilized.
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+----------------------+----------+---------------------------------+
| Location in | Protocol | Used to Protect |
| Architecture | | |
+----------------------+----------+---------------------------------+
| WTP To Access | IPSec | Authenticity of Management, |
| Controller Service | | session keys, user traffic |
| (Section 4) | | |
+----------------------+----------+---------------------------------+
| Authenticator to AAA | IPSec | Authenticity and |
| Service (Section 6) | | Confidentiality of AAA traffic |
| | | (wrapped session keys) |
+----------------------+----------+---------------------------------+
Table 10: IPSEC Architectural Usage
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9. Security Considerations
The cryptographic security level of a complex system is limited to
that of the weakest component in the system. The use of 128-bit
block ciphers with 128-bit keys is now common, but in many systems,
the security is limited by other factors, such as public keys with a
strength of just 80 bits, or keys that are manually configured. A
typical security protocol uses multiple cryptographic algorithms to
achieve different security goals: encryption to provide
confidentiality, data authentication to protect the integrity of
data, key derivation to provide the keys for those algorithms, key
establishment to determine shared keys, and digital signatures to
authenticate the entity on the other end of the wire. In order to
provide a high security level, a protocol needs to use algorithms and
parameters that consistently meet that security goal. Wireless
systems use multiple security protocols, thus requiring consistency
across multiple protocols. To achieve consistency, one must first
understand all of the cryptographic components in a wireless system.
This note makes that process easier, by cataloging the components
that appear in typical wireless architectures.
It is also important to note that not all secrets are equal. A
secret which gives you access to data for a short period of time
might be considered less important than one that exposes data for a
longer period of time. Depending on the system being built and
associated security constraints, the value of the secret being
protected can inform appropriate choices for the cryptographic
strength over sub components of a wireless architecture.
Finally, this note is intended to encourage the use of consistent
cryptographic strengths of confidentiality, integrity and
authenticity within the entire wireless LAN architecture. While
profiles of this document might justify inconsistent algorithm
strength choices, the profiles need to use cryptography throughout
the architecture to provide end-to-end security.
9.1. Algorithm Choices
The choices of the algorithms to use in this document are left to the
profile authors discretion. However, it must be clear that profiles
need to avoid the use of known broken cryptographic algorithms (i.e.
WEP, TKIP, etc).
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10. IANA Considerations
None
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11. Acknowledgements
The authors would like to acknowledge David McGrew, Nancy Cam-Winget
and Carlos Pignataro for their constructive comments on this
document.
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12. References
12.1. Normative References
[IEEE.802-11.2012]
"IEEE Standard for Information technology--
Telecommunications and information exchange between
systems-- Local and metropolitan area networks-- Specific
requirements Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) Specifications",
March 2012, <http://standards.ieee.org/getieee802/
download/802.11-2012.pdf>.
[IEEE.802-1X.2010]
"IEEE Standard for Local and metropolitan area networks -
Port-Based Network Access Control", 2010, <http://
standards.ieee.org/getieee802/download/802.1X-2010.pdf>.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC5415] Calhoun, P., Montemurro, M., and D. Stanley, "Control And
Provisioning of Wireless Access Points (CAPWAP) Protocol
Specification", RFC 5415, March 2009.
12.2. Informative References
[AES_Key_Wrap]
"", <http://csrc.nist.gov/groups/ST/toolkit/documents/kms/
key-wrap.pdf>.
[FIPS-180-3]
FIPS Publication 180-3, "Secured Hash Standard",
FIPS 180-3, October 2008.
[FIPS.197.2001]
National Institute of Standards and Technology, "Advanced
Encryption Standard (AES)", FIPS PUB 197, November 2001, <
http://csrc.nist.gov/publications/fips/fips197/
fips-197.pdf>.
[NIST.PUB.198A]
National Institute of Standards and Technology, "The
Keyed-Hash Message Authentication Code (HMAC)", FIPS PUB
198A, March 2002, <http://csrc.nist.gov/publications/fips/
fips198/fips-198a.pdf>.
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[NIST800-57]
Barker, E., Barker, W., Burr, W., Polk, W., and M. Smid,
"Recommendations for Key Management", NIST SP 800-57,
March 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, September 2002.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
Diffie-Hellman groups for Internet Key Exchange (IKE)",
RFC 3526, May 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[RFC4017] Stanley, D., Walker, J., and B. Aboba, "Extensible
Authentication Protocol (EAP) Method Requirements for
Wireless LANs", RFC 4017, March 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
384, and HMAC-SHA-512 with IPsec", RFC 4868, May 2007.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible
Authentication Protocol (EAP) Key Management Framework",
RFC 5247, August 2008.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
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Security Version 1.2", RFC 6347, January 2012.
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Authors' Addresses
Stephen M. Orr
Cisco Systems, Inc.
1 Paragon Drive
Suite 275
Montvale, NJ 07645
US
Email: sorr@cisco.com
Anthony H. Grieco
Cisco Systems, Inc.
7025 Kit Creek Road
RTP, NC 27709
US
Email: agrieco@cisco.com
Dan Harkins
Aruba Networks
1322 Crossman ave
Sunnyvale, CA 94089
US
Email: dharkins@arubanetworks.com
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